I'm interested in chatting to anyone who has fitted the Kinetics kit. The rear triangle looks simple enough to replace and I am confident with the Rohloff setup as I recently replaced the shifter and cables on my Thorn Rohloff without problems. Kinetics mention they sometimes have problems unfastening the hinge bolts but I tried mine and they are not stuck.
I do not own a Kinetic Rohloff Brompton but I have ridden one. The bike was converted by Ben in his workshop and the owner is very happy with it - it also has the front fork and disk brakes. I consider the rear triangle good engineering (personally I'd go for the version with integrated rack but that's a matter of taste) and would assume the swap is not different from an ordinary swap of the rear triangle or a change of the rear hinge bolt. It is however a bit of an expert job.
Regarding the Rohloff on the Brommi: I do own a couple of bikes with a Rohloff hub and this is for a reason. The thing is bullet proof, close to maintenance free and never let me down. And for me clearly the best of all geared hubs currently available, avoiding the downsides of derailleur setups while being almost as efficient. For the Brommi however I considered it to be an overdose (and to a degree still do). Just that I do not like the alternatives too much including the Alfine 11. So in the meantime I own a Rohloff Brompton, too. It is definitively a bit of an overdose as I never needed the lowest gears until today (which obviously depends from the terrain you are riding), it is expensive, it is heavy and my 2-speed is way faster and much lighter, so I clearly prefer it in everyday life and for my commute. But for a touring setup I'd consider the Rohloff a good choice. Not necessary and a bit of a luxury, but hey. Typically with 50/13 or 54/13.
Regarding the sourcing: Ben is a bit famous for deadlines and delivery times passing by. I've never dealt with him personally but have heard endless stories from people who have. But he is a honest and nice guy as people agree and the things he makes are solid and good work. Just that it may take a loooooong time until your order is done - he is a one man band and has a lot of work, so things are not always running smoothly in regards of communication and time scheduling. So possibly it helps to be a
very relaxed person to deal with him.

Other than that you can buy his rear triangele from SJS as well - they do sell Kinetics parts. Stock and color vary but they are usually delivering fast if they have the desired item in stock.
There is also a ti-triangle for the Rohloff available from Vostok, in case you want to go for alternatives.